Bachelor party - invite bride's younger brother?

I've been tasked with throwing a bachelor party for a friend of mine. He'd like to include a few of the bride's friends and family as well. Her youngest brother is just turning 18.

Question is: is that too young for a bachelor party? Is it normal to invite brides' friends and families?

If they are part of the wedding party, then sure. But since the groom asked you to invite them, you should. For the younger brother, it depends on where you're going. If you're doing a golf trip, then sure, bring him. If you're going to Vegas, then leave him at home (he can't do anything anyway).

My under 18 bro who was a GM in my wedding was invited to DH's bachelor party. He didn't go to the evening "entertainment" but he went bowling, go-cart racing & dinner w/ them.